A solid-state imaging device (camera module) which is applied to a camera phone and a digital still camera is normally arranged such that a solid-state image sensor, a digital signal processor (DSP), a lens, a lens holder (housing), a lens barrel, etc. are integrated into a package. In addition, recently, a mechanical part for providing a focusing function such as autofocus (AF) and zoom functions with the solid-state imaging device is bonded and fixed to a wiring board or any other part of the solid-state imaging device with adhesive.
Conventionally, the mechanical part for providing the focusing function is bonded to its counterpart to be bonded to the mechanical part with the adhesive applied on either the mechanical part or the counterpart. For example, the adhesive is applied to a bonding surface by using an application nozzle in such a manner that the application nozzle scans the bonding surface of either part with one stroke.
After the application of the adhesive, a bond of the mechanical part for providing the focusing function is completed by hardening the adhesive with the both parts kept in contact with each other tightly.
However, in such a bond, excess adhesive may be squeezed out of the bonding surface. On the other hand, a shortage of applied adhesive may result in an adhesion failure. Thus, it is difficult to adjust an application amount of the adhesive, especially for a camera module which is applied to a cellular phone.
In view of the problem, for example, Patent Document 1 discloses an art of an image sensor module. The art aims at preventing the adhesive from being applied unevenly and being squeezed out of the bonding surface. FIG. 14 is a cross-sectional view of the image sensor module of Patent Document 1. An image sensor module 500 in FIG. 14 includes grooves 514 each of which is provided on a part of the bonding surface of a lens holder 511 (the lens holder 511 is to be adhered with a wiring board 515 at the bonding surface). The lens holder 511 is fixed to the wiring board 515 by the adhesive which fills the grooves 514. Specifically, by filling the grooves 514 with the adhesive while the lens holder 511 and the wiring board 515 being appressed against each other, the lens holder 511 and the wiring board 515 are joined and fixed to each other. This arrangement of Patent Document 1 thus prevents the adhesive from being applied unevenly and thereby improves quality and workability of the bonding. Also, this arrangement prevents the adhesive from being squeezed out of the bonding surface.
Patent Document 1 also discloses that the same effect as the arrangement with the grooves 514 can be obtained from another arrangement such that the adhesive fills a taper section (not shown in figures), instead of the grooves 514, which taper section is formed on lateral sides to the bottom base of the lens holder 511.
<Patent Document 1>
Japanese Unexamined Patent Publication No. 236754/2005 (Tokukai 2005-236754 (Date of publication: Sep. 2, 2005))
However, the image sensor module of Patent Document 1 has a problem that adhesive strength is insufficient.
According to Patent Document 1, specifically, the adhesive fills only the grooves 514 as illustrated in FIG. 14. With this arrangement, improvement in the quality of the bond can be expected to a certain extent by avoiding an uneven application of the adhesive.
According to Patent Document 1, the adhesive fills the grooves 514 with the lens holder 511 and the wiring board 515 appressed against each other. As a result, the lens holder 511 and the wiring board 515 are bonded to each other only by the adhesive which fills the grooves 514. That is, the adhesive is not supplied to a part without the groove 514. Accordingly, adhesive strength is very low because a part involved in the bond is limited to the groove 514. A low adhesive strength allows the mechanical part for providing the focusing function (autofocus function or zoom function) to come easily off from the lens holder 511 after the bond thereto. Therefore, in a case where the mechanical part is incorporated in a cellular phone or a digital still camera, the mechanical part may come off therefrom especially when the phone or the camera are dropped. Such a problem also arises in a case where the taper section is formed instead of the grooves 514.